The present invention relates to processing to adapt audio equalization to an environment, and in particular to determining the Signal to Noise Ratio (SNR) from a measurement and ensuring that the SNR supports the audio equalization processing.
The accuracy of sound reproduction is often degraded by sound reflections from surfaces within a listening space. Methods have been developed to compensate for the effects of these sound reflections. Such methods require transmitting a test signal and measuring the resulting sound at one or more location in the listening space. Unfortunately, the ability to accurately measure the sound reflections requires a minimum SNR to distinguish the sound reflections from noise in the listening space. While it is generally possible to increase the level of the test signal, at some level, the test signal becomes objectionable to individuals in or near the listening space, or exceeds the sound level accurately produced by speakers used to generate the test signal. Thus, a method is needed to measure the background noise present in the listening space to determine an adequate level for the test signal.
Sound from different speakers may arrive at the listener at different times due to varying distances of the speakers, different electronics in the speakers or differences in the signal path, e.g., wireless links or amplifiers with different latency. The delays may be measured and compensated for to provide more accurate sound. If a minimum signal to noise ratios is not achieved, the compensation may experience reduced accuracy or fail.
Speaker sensitivities perceived at a listening position may be measured and the measurements used to adjust output trim levels to align the absolute sensitivity to a reference sensitivity from available home theater standards. If a minimum signal to noise ratios is not achieved, the alignment may experience reduced accuracy or fail.
Known methods for measuring the background noise do so separately before transmitting the test signal to measure the listening space and are slow. Such methods are not able to detect extra background noise intrusions that occur during the room measurement process.